Ended prematurely

This is a randomized, double-blind, single center study in healthy volunteers dosed to steady state with betrixaban, designed to (1) Determine an andexanet dosing regimen required to reverse anticoagulant activity of betrixaban in healthy subjects, (2) Assess the safety and tolerability of andexanet vs. placebo (3) Determine the PK properties of andexanet and betrixaban (4) Determine the PD properties of betrixaban before, during, and after receiving andexanet or placebo and (5) Investigate the immunogenicity of andexanet in the presence of betrixaban.

Inclusion Criteria:

1. The subject is a healthy man or woman between the ages of 18 and 45 years old, inclusive, who agrees to comply with the contraception and reproduction restrictions of the study:

   Men must be using two acceptable methods of contraception, at least one of which must be a barrier method (e.g., spermicidal gel plus condom) for the entire duration of the study and for at least three months following last study drug administration, and refrain from attempting to father a child or donating sperm in the three (3) months following the last study drug administration. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception.

   OR Men who report surgical sterilization (e.g., bilateral vasectomy) must have had the procedure at least six (6) months prior to initial dosing. Surgical sterilization procedures should be supported with clinical documentation and noted in the Relevant Medical History/Current Medical Conditions section of the Case report forms (CRFs).

   Women of childbearing potential must be using two medically acceptable methods of contraception, at least one of which must be a barrier method, (e.g., intra-uterine device plus condom, spermicidal gel plus condom, diaphragm plus condom, etc.), from the time of screening and for the duration of the study, through at least three months following last study drug administration. NOTE: Oral contraceptive use is not permitted due to their increased risk of thromboembolism. Periodic abstinence (e.g., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception.

   OR Postmenopausal women must have had no regular menstrual bleeding for at least one (1) year prior to initial dosing. Menopause will be confirmed by an elevated plasma Follicle-stimulating hormone (FSH) level > 40mIU/mL at screening for women not in receipt of hormone replacement therapy (HRT); OR Women who report surgical sterilization (i.e., hysterectomy and/or bilateral oophorectomy) must have had the procedure at least six (6) months prior to initial dosing. Surgical sterilization procedures should be supported with clinical documentation and noted in the Relevant Medical History/Current Medical Conditions section of the CRF.

   AND All women must have a documented negative pregnancy test result at screening and at baseline.

2. The subject has clinically unremarkable medical history, physical examination, ECG, and vital signs, as determined by the Investigator. Laboratory values must also be clinically unremarkable as determined by the Investigator, with the exception of the following labs which must be strictly within the normal range:

   1. Coagulation labs - PT, aPTT, ACT;
   2. Hematology lab - Hematocrit/Hemoglobin;
   3. Liver function labs - Aspartate aminotransferase (AST)/alanine aminotransferase (ALT) (may be below lower limit of normal [LLN], but not above upper limit of normal [ULN]).

3. The subject has a body mass index 19 to 30 kg/m2, inclusive, and weighs at least 60 kg.

4. The subject agrees to abstain from alcohol consumption for 48 hours prior to dosing and for the duration of the in-house study period.

5. The subject smokes <4 cigarettes/day (or equivalent: ≤0.5 can of chewing tobacco/week, 1 cigar/day) and agrees to abstain from smoking while domiciled.

6. The subject is able to read and give written informed consent and has signed a consent form approved by the Investigator's Institutional Review Board (IRB) or Ethics Committee (EC).

Exclusion Criteria:

1. The subject has a known history (including family history) of, symptoms of, or risk factors for bleeding (e.g., prior gastrointestinal bleeding, known berry aneurysm/ vascular malformation) or a stool specimen within 6 months of randomization that is positive for occult blood.
2. The subject has an absolute/relative contraindication to anticoagulation.
3. The subject has a history (including family history) of or risk factors for a hypercoagulable or thrombotic condition (e.g., deep vein thrombosis/pulmonary embolism, Factor V Leiden carrier).
4. The subject has a history of any clinically significant (as determined by the Investigator) cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal, or other major disease or condition which is known to make the subject susceptible to volume overload.
5. The subject has taken any prescription drugs (including oral contraceptives/HRT) or illicit drugs in the 30 days prior to randomization. The subject is also excluded if he/she has taken over the counter drugs, including dietary supplements and herbal products, in the 2 weeks prior to randomization. Furthermore, the subject agrees not to take any such drugs throughout the study (if it becomes medically necessary to do so, the Investigator and Portola Medical Monitor must be informed immediately).
6. The subject has a history of major surgery, severe trauma or bone fracture within 3 months prior to dosing; or planned surgery within 1 month after dosing.
7. The subject has a history of blood donation of more than 500 mL within 3 months prior to dosing.
8. The subject has participated in an investigational drug study within 30 days or 5 half-lives of the investigational compound, whichever is greater, of Day -1.
9. The subject has a positive screen for drugs of abuse at Day -1.
10. The subject has a medical or surgical condition which may impair drug absorption.
11. The subject is allergic to any of the vehicle ingredients: tris, arginine, hydrochloric acid, sucrose and polysorbate 80.
12. Subject is breastfeeding.
13. The subject has any condition which could interfere with or for which the treatment might interfere with the conduct of the study, or which would, in the opinion of the Investigator increase the risk of the subject's participation in the study. This would include, but is not limited to alcoholism, drug dependency or abuse, psychiatric disease, epilepsy or any unexplained blackouts.

The safety population will consist of all subjects randomized and treated with at least one dose of study medication (andexanet, andexanet placebo, or betrixaban). All safety analyses will be performed by actual treatment received.

Study day 1 to 48(+3)

AEs, both serious and non-serious, occurring between signing informed consent and through the Termination Visit will be recorded on the eCRFs. All AEs/SAEs should be monitored until they are resolved, are not expected to improve further, or are determined to be due to a stable or chronic condition or intercurrent illness. Any AE/SAE that occurs with an onset date > 30 days after study completion and that the Investigator considers to be related to study medication, must be reported to Portola.

Double Blind